The French government sought to bolster the case for military action against Syria last night, releasing a declassified summary of French intelligence that links president Bashar Assad’s government to the apparent use of chemical weapons outside Damascus last month.

The report comes as the French public’s apprehension about intervening in Syria is mounting. President Barack Obama’s announcement that he would seek congressional approval for US military strikes, paired with the British parliament’s vote against taking part, has left France somewhat isolated on the issue internationally. There are rising calls for a parliamentary vote in France, too, though the French president, Francois Hollande, has no constitutional duty to consult the legislature before authorising the use of military force and his government has said it does not intend to do so.

The nine-page intelligence summary, which included proprietary French intelligence in addition to analyses of publicly circulated videos and information shared by allied intelligence services, was published on government websites Monday evening. It asserts that Dr Assad’s forces conducted attacks involving the “massive use of chemical agents” against civilian populations in several suburbs of Damascus on August 21st, and later mounted “significant ground and aerial strikes” with conventional munitions that were aimed at the “destruction of evidence” in those areas. The report gave no indication , however, as to the level of certitude of the conclusions presented.

“Our services possess information, from a national source, that leave one to think that other actions of this nature could again be conducted,” the report claimed, though it provided no further detail. It said that none of the rebel groups fighting the Syrian government now possessed the “capacity to stock and use” such chemical agents.

Dr Assad has rejected all assertions that his government was responsible for those attacks. In excerpts from an interview with Le Figaro published online yesterday evening, he said that neither France nor the United States had advanced “a single piece of evidence” linking his government to chemical weapons use, and that a strike on his country would have unknowable consequences. The Middle East is “a powder keg, and the flame is approaching it today,” he said in the interview. “Everyone will lose control of the situation when the powder keg explodes. Chaos and extremism will spread. The risk of a regional war exists.”

There was widespread consensus among French officials that the Assad government was culpable even before the intelligence report was published Monday, however, so it was not clear what impact the document would have. The lower house of the French parliament has scheduled a special session about Syria tomorrow, but no vote is planned. Several government ministers, including prime minister Jean-Marc Ayrault, met with senior legislators yesterday.

The leader of the opposition in parliament, Christian Jacob, said afterward that an intervention “could only be justified in the framework of the United Nations. ” He expressed concern that France was out of step with its neighbours, including Germany, which has made clear that it would participate militarily only in operations backed by the United Nations. “Why is there no European country, not a single European country as an ally?” he asked.

Alain Juppé, a former prime minister and foreign minister, said in a speech yesterday that “even if the Constitution does not require it, I think that in such a context, the parliament should express itself by a vote, so that the president of the republic can at least rely upon the backing of the national representation.”

Mr Juppé called upon Mr Hollande to publicly detail his strategy for intervention. Some on the left have issued similar calls, including the Greens party and a small number of Socialists, as well as the leftist national newspaper Libération. “After the British dropping out and Barack Obama’s sudden rediscovery of his Congress, Francois Hollande finds himself quite alone in wanting to hold his war in Syria,” the newspaper said in an editorial. Under France’s “monarchic constitution,” the president has “every power to make war,” Libération acknowledged. “But can he today be the only head of state to employ force without a vote of the national representation, without even a speech?”

Mr Hollande, a Socialist, is backed by majorities in both houses of Parliament. Though recent polls indicate that the French public opposes intervention in Syria by a narrow margin, most legislators are thought to favor it. Mr Hollande has notably received the public support of the leader of the center-right Union for a Popular Movement party, Jean-Francois Copé. “In this blocked situation” in Syria, Mr Copé said in an interview published in Le Monde, “the first urgent priority is to react in an extremely firm manner in the face of what I view as the unacceptable. The use of chemical gas, if proven, constitutes a crime against humanity.”

French officials say they will await the decision of the US Congress before taking any action, however, not least because France and other Nato allies usually depend on American logistical support for operations overseas. Still, a decision by Washington against intervention would not “call into question the principle of a sanction” against the Assad government, said Romain Nadal, a diplomatic spokesman for Mr Hollande. “France will not act alone,” however, and would seek an alternative coalition, Mr Nadal said. Its possible composition was not clear.

The French intelligence report released yesterday largely matched the conclusions of an unclassified summary of US intelligence released Friday, which linked the Syrian government to the chemical attack with “high certainty.” The US government said the attack killed at least 1,429 people.

Though much of the debate in France has been focused on the role of parliament, there are also growing doubts about the wisdom of any military intervention. “It is not France’s place to intervene in Syria,” the rightist newspaper Le Figaro said Monday in an editorial. “Does one know what chain reaction an intervention, even initially ‘proportionate,’ will set off?”

To respond to the Damascus chemical attack with airstrikes “would be to fall into Dr Assad’s trap,” the newspaper wrote. It recommended instead that France “put a bit of coherence in our Syrian policy,” but it did not elaborate.